Sound-box construction



Aprifi 1936. BE D v 2,036,98Q

SOUND BOX CONSTRUCTION inal Filed Aug.,8, 1931 [N VE/VTOR 725000195 /7BEA PD ATTORNEY Patented Apr. 7, 1936 UNITED STATES PATENT OFFICESOUND-BOX CONSTRUCTION Theodore H. Beard, Bridgeport, Conn, assignor toDictaphone Corporation,New York, N. Y., a corporation of New York 7Claims. (Cl. 27427) This invention relates to sound-boxes and moreparticularly sound-boxes such as are employed for recording sounds upona cylindrical Wax record blank.

One of the defects inherent in such soundboxes as have been heretoforeused for the recording of compound sound waves such as are produced bythe human voice, or by musical instruments, is the tendency to respondstrongly to sound waves of relatively low frequency and weakly orinefficiently to sound waves of relatively high frequency. When a recordmade under these conditions is reproduced, the sounds produced seem tobe lower in tone than the sounds recorded, and have lost many of theirquality or personality characteristics. A well-known example of thisdefect is the reproduction of a wax cylinder record of the human voice.Through the loss of many of the higher wave frequencies and apparentexaggeration of the sound waves of low frequency, the record whenreproduced sounds unnatural and the voice is often unrecognizable. Alsothe general audible effeet is poor, and the reproduction unsatisfactory,often being so dull and muffled as to be almost unintelligible. This iseasily understood when it is remember what a large part the highfrequency overtones have to play in determining the characteristicqualities of the voice.

It is believed that the cause of the loss of the higher wave frequenciesin recording is due to the fact that the energy of speech residesprincipally in the frequencies below 1000 cycles per second and thatarticulation and intelligibility reside mostly in the higher frequencysounds, those above 1000 cycles per second. Consequently the diaphragmof the sound box, responding with greater amplitude to the low frequencysounds, produces a record in which these sounds predominate.

Another objectionable feature of the usual type of sound-box is thetendency of the diaphragm to blast when a strong or loud voice isrecorded. This seems to be due to the fact that the force of the loudvoice or musical note, as the case may be, is greater than theresponsive capacity of the diaphragm. A fluttering of the diaphragmresults which in a recorder produces breaks in what should be a smoothlycontinuous hill-and-dale track formed upon the record-cylinder surface.When the reproducing stylus, in reproducing the record, travels overthis portion thereof, it produces a harsh and foreign noise, in additionto a distorted reproduction of the original sound. Not only is the soundor note more or less imperfectly reproduced, but the sound occasioned bythe concussion of the sapphire against the abrupt edges of the breaks inthe record track, is concurrent therewith.

It is usually desirable to get considerable vol-' ume, and this may bestbe attained by the use of comparatively thin diaphragms, which,unfortunately, are more susceptible to blast than those of greatersubstance.

It is an object of the present invention to provide a sound-box capableof producing a record substantially free from the evils of blasting,even when sound waves of relatively great amplitude are impressed uponthe diaghram. Another object is to provide means adapted to preventblasting even when diaphragms of exceptional thinness are mounted in thesound-box.

Another object is to provide a device of the nature described capable ofrecording and reproducing in a highly natural manner. Another object isto increase the voice or tonal range of a sound-box adapted either torecord or reproduce.

Another object is to provide an instrument of the character describedadapted to attain sharp and clear reproduction of sounds throughout awide range of wave frequencies.

Another object is to produce a simple and rugged device of the abovenature. Another object is to provide a device of the nature describedeasily adjustable-to adapt it for efficiently re- 30 cording orreproducing sounds of varying loudness and tonal range.

Other objects will be in part obvious and in part pointed outhereinafter.

The invention accordingly consists in the features of construction,combinations of elements, and arrangementsof parts as will beexemplified in the structure to be hereinafter described and the scopeof the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of the variouspossible embodiments of my invention:

Fig. 1 is a side elevation of a sound-box of a well known type, showinga portion of the tonearm and disclosing a feature of my invention;

Fig. 2 is a plan View thereof; and

Fig. 3 is a cross section taken on line 33 of Fig. 2.

Similar reference characters refer to similar parts throughout thevarious views of the drawmg.

The sound-box shown in the present embodiment of my invention involvesthe use of a sound wave baflle and leak-off. Referring to the drawingthe sound-box structure comprises a tonearm or tube I closed at its end,as by the wall 2 and which is provided with a downwardly turned flange 3surrounding a circular opening 4. The pan or sound-box head comprises ashallow inverted dishlike member 5 having circumferential walls 6. Thecircular edge 1 of an opening formed in the center of the pan is seatedin and secured to the tone-tube by turning the flange 3 over said edge,as at 8, as shown in my present construction, although it will beunderstood that the tone-arm and pan may be formed integrally. Such anintegral construction is shown in the patent'to .Bodine .et 'al., No.

1,606,744, to which reference is made for a de-' scription of the mannerin which a combined recorder and reproducer maybe mounted, and

an explanation of its mode of operation as applied to a commercialdictating machine.

The pan is further supported by a boss 9 formed on the tone-arm I towhich the pan is attached by means of a screw H). A diaphragm II issuitably mounted in the sound head, as by means of gaskets 12-1-3, whichin the present construction are held in place by means of a fillet Hi ofplastic material such as beeswax. The diaphragm is preferably made ofmica, perforated at its cen ter for the passage of a small screw 15,which is threaded into and makes fast to the diaphragm a stylus or pointholder 16. Holder I6 is further supported upon the diaphragm by means ofan arm ll having an offset portion 18, which, in assembling, is passedthrough a perforation in the diaphragm, as at 1'9. The stylus holder isof familiar form and provides a seat for a recording stylus 2'0 and areproducing stylus 2|, either of which may be brought into operativeengagement with a record-cylinder, by means shown and described in theBodine patent referred to above.

No novelty is claimed for the features thus far described.

The upper wall of the tone-arm is perforated, as by'punching orotherwise, at a point directly opposite the center-of the opening 4, andthe portions 22 of the wall, which are inturned by the punch, areinternally threaded to receive a solid threaded plug 23 terminating inan enlarged conical end 24 which extends downwardly through the opening4 into close proximity to the diaphragm. A slot 25 formed in the upperend of the plug is adapted to receive a screw driver 'by means of whichthe position of the plug may beadjusted by screwing it in or out of thesound-box. This adjustment permits of varying the clearance between thebase of its conical end and the diaphragm, and also permits control ofthe size of the annular portion of opening 4 surrounding the cone. Theobject of this plug member is to prevent the impinging of sound wavesdirectly at the center of. the diaphragm and to cause them to strike anannular portion of the diaphragm adjacent the periphery thereof, and hasother objects as will presently appear.

The result of this limitation of impact appears to be twofold. In thefirst place it serves to prevent blasting and thus ensures the tracing-of a smoothly continuous track upon a record-cylinder during recording.This result permits the use of thinner diaphragms, from which it followsthat a tone of a certain intensity will produce sound wave tracks uponthe record of greater amplitude; and greater volume is attained when therecord is reproduced.

And secondly, it has been found that the defiection of the sound wavesaccomplished by the conical plug tones down the effect produced upon thediaphragm by vibrations of lower frequency and permits it to respondmore accurately to vibrations of higher frequency, thus enabling arecord to be made of these higher frequency waves and a consequentimprovement of the quality of the tone and the attainment of a higherpitch when the record is reproduced.

Many tests of the standard type of recorderreproducer, in which theconical plug is omitted,

establishes the fact that it is naturally responsive to sounds up to'2500 cycles per second and, with increasing weakness, to sounds up to4000 cycles per second. On the other hand, tests with soundboxes inwhich :theconical plug was used showed that they were naturallyresponsive to sounds of 3500 cycles per second and, with increasingweakness, to sounds up to 5000 cycles per second. As would be expected,this resulted in more natural recording and reproducing, in that therewere saved many overtones and other characteristics which determinetimbre or voice personality. This result .is believed to be in part dueto the damping effect of the air cushion established between the end ofthe solid plug and the center of the diaphragm, which aids in preventingblastin'g and makes the diaphragm more responsive to sound waves ofhigher frequency.

But a further improvement in the action of the device when used as arecorder has been effected by the provision of a leak-off passage 26 inthe'for-m of a perforation extending through the end wall 2 of thetone-arm I. This passage connects with the interior of the sound-box ata point above the annular opening formed between the conical end of theplug and the rim of the opening 4.

The chief benefit derived from the leak-off seems to be that by its usethe recorder is able to handle with .substantially equal efficiencyvibrations covering a wide range of intensity. The excess energy of aloud voice is drained off to the surrounding atmosphere so that thediaphragm is not put under an overstrain. This prevents rattle and blastof the diaphragm and ensures the production of a good record.-

Waves of low frequency which have a larger share of the energy of speechthan those of high frequency, are leaked off to a greater extent thanare the latter, and thus the leak-off passage aids the baffling anddamping efiects of the plug in effecting the recording of more of thehigher overtones or partials of the voice and so enhance the quality ofreproduction.

It willbe seen that there is provided a construction of an essentiallypractical nature in which the several objects of this invention areattained.

As many possible embodiments may be made of the above invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawing is to beinterpreted as illustrative and not in a limiting sense.

I claim as my invention:

1.. In a dictating machine, in combination, a tone-tube closed at itsend by a wall and having an outlet opening disposed in a planesubstantially normal to said wall, a sound-box connected with saidtone-tube at said opening, a conical plug mounted in the wall of saidtube opposite said opening and extending into said opening,

means for shifting said plug to vary the size.

of the unobstructed area of said opening, and a leak-off port providedin the said end wall of said tube.

2. In a dictating machine, in combination, a tone-tube closed at its endby a wall and having an outlet opening disposed in a plane substantiallynormal to said wall, a sound-box connected with said tone-tube at saidopening, a stud threaded into the wall of said tube opposite saidopening and having a conical head extending through said opening intosaid sound-box, and a leak-off port in the said end wall of said tube.

3. In a dictation-recording machine, in combination, a tone-tube havinga closed end and an opening adjacent said end, the axes of said tube andopening being substantially normal to each other, a sound-box secured tosaid tone-tube at said opening, a diaphragm in said sound-box supportinga recording stylus, a solid conical plug mounted in the wall of saidtube and extending into said opening, the base of said plug beingdirected toward said diaphragm, and a leak-01f port provided in a wallof said tube adjacent said opening.

4. In a dictating machine, in combination, a tone-tube closed at its endby a wall and having an outlet opening disposed in a plane substantiallynormal to said wall, a sound-box connected with said tone-tube at saidopening, and a plug mounted in the wall of said tube opposite saidopening and extending into said opening, and a leak-off port in the endwall of said tone-tube.

5. In a dictating machine, a sound-box, a tonetube connecting with theinterior of said soundbox through a circular opening, a conical plughaving a diameter at its base substantially equal to the diameter ofsaid opening mounted concentrically in said opening to provide agradually expanding annular passage connecting the interior of saidsound-box with said tone-tube, means for shifting said plug to vary thesize of the unobstructed area of said opening, and a leakoff port in aportion of the wall of said tone-tube in close proximity to said conicalplug.

6. In a dictation recording machine, in combination, a sound-box, astylus actuating diaphragm, a tone-tube connecting with the interior ofsaid sound-box through an opening, a leakoff port in said tone-tube, anda wave-baffle positioned in said opening operatively to coact with saidleak-off port in effecting at said diaphragm a controlled balance of theenergies of sound wave components of widely difierent frequencies.

7. In a dictating machine, a sound-box, a tonetube connecting with theinterior of said soundbox through a circular opening, a conical plughaving a diameter at its base substantially equal to the diameter ofsaid opening mounted concentrically in said opening to provide agradually expanding annular passage connecting the interior of saidsound-box with said tone-tube, and means for shifting said plug to varythe size of the unobstructed opening of said area.

THEODORE H. BEARD.

